Trichloroethene (TCE) and tetrachloroethene (perchloroethene, PCE) are the most commonly used industrial solvents and degreasers in the world. The annual U.S. consumption of TCE was 245 million pounds in 2005, with a 4.5% per year increase since then. As a consequence of its extensive use, spillage and improper disposal have resulted, and thus TCE is one of the most commonly found chemicals in contaminated sites. About 34% of the drinking water sources and most groundwater contamination sites are estimated to contain TCE, and 75% of EPA National Priority List hazardous waste sites and Superfund sites have TCE pollution. TCE is a suspected carcinogen, as well as a known kidney and liver toxin. In addition, TCE can be transformed to vinyl chloride via microbial anaerobic dehalogenation in groundwater, increasing the concerns regarding TCE contamination in groundwater.
TCE concentration measurement using gas chromatography (GC) is the most popular TCE detection method with good selectivity and low limits of detection (LOD), as low as 0.02 μg/L using EPA method 8260b for volatile organic compounds, while absorption spectroscopy based techniques (e.g., Fourier transform infrared spectroscopy) can also detect trace amounts of TCE with short acquisition times and high signal-to-noise ratios. However, these methods are time-consuming and expensive, and additional pretreatment steps are often required prior to sample analysis.
Biosensors have the potential to be excellent alternatives or complements to traditional analytical chemical methods for environmental monitoring. By integrating a biological process and transduction, a biosensor is capable of real-time analysis with simplicity of operation. In a biosensor system, enzymes have benefits as the biocomponents due to their high sensitivity and good specificity, while optical transduction has potential advantages over electrical transduction in environmental monitoring because of low signal losses over long distance as well as not requiring a reference signal. Biosensors are often reagentless, and can thus provide continuous, in-situ measurements as a cost-effective alternative compared with traditional analytical methods.